Shortly before taking over the National Theatre, Richard Eyre tried, and failed, to adapt the classic film musical High Society for the stage in a 1987 production that he both directed and scripted at the Victoria Palace. In 1998, the Broadway playwright Arthur Kopit made another attempt for a version that opened at New York's St James Theatre, but it wasn't a success either.

Is it third time lucky as that latter version now returns to London for its premiere at Regent's Park's Open Air Theatre? I'd like to say yes, because this is a venue that encourages generosity, but my rapture has to be qualified.

It would take a curmudgeon not to enjoy a show here - especially one that's graced by an irresistible set of Cole Porter songs. As well as the scintillating "Who Wants to be a Millionaire?" and "Well, Did You Evah?" and the romantic "True Love" and "You're Sensational" that you'll remember from the movie, other Porter classics are interpolated here, including "Let's Misbehave" (dropped from 1928's Paris) and "Just One of Those Things" (from 1935's Jubilee).

But while these may be as effervescent as champagne, Kopit's book for the musical threatens to be as flat as a bottle of coke left open overnight. The movie of High Society fizzes partly because of the quartet of amazing leads (Grace Kelly, Bing Crosby, Frank Sinatra and Celeste Holm), but also because of its respect for the classic Philip Barry play, The Philadelphia Story, that it's based on.

For the stage version, the flavour is more akin to a PG Wodehouse or George S Kaufman musical farce script (though without the redeeming jokes), as it laboriously lays out the convoluted plot between the songs. Unlike the best modern musical songs, Porter's songs don't function to advance plot but instead provide respite in the delight of their wordplay.

Kopit's scheme is to amplify the social context and snobbery of the story. The imminent nuptials of heiress Tracy Lord (the tall, striking Annette McLaughlin) are set against the background of her previous failed marriage and that of her parents, rocked by dad's affair with an actress - all variously fuelled by alcohol dependencies. The musical also provides a singing-and-dancing chorus of maids and menservants to comment sardonically on what their 'betters' are up to.

Ian Talbot's appealing production provides what comic energy it can in the heavy-going circumstances, particularly in the hilarious performances of Tracie Bennett, as one half of a pair of tabloid magazine hacks who gatecrash the wedding, and Brian Green, as her rambunctious admirer Uncle Willie.

But if they find the right comic notes, Hal Fowler's Mike Connor (the other hack) is the only one in the company to find the true musical ones. There was a time when British musicals used to be quaintly ill-sung, and Dale Rapley as the romantic lead Dexter is a reminder of it.

- Mark Shenton